Is it normal that i don't notice the gender of somebody's pet dog?

I am a contractor doing small jobs on other people's properties. Most of my customers have dogs. I am not a fan of domestic pets. They annoy me, so I usually ignore them. I'm NOT an animal hater, and I'm NOT mean to them. I just simply prefer to ignore them and wish they would do the same to me. Because I usually don't pay much attention to the dogs I rarely even notice if the dog is male or female, and I don't care.
The problem is that sometimes when I'm speaking to my customer the conversation might turn to the dog, at which time I may refer to the dog as "he", without really knowing what gender it is. Other times, on the same job, I could just as easily refer to the dog as "she". On such a job my customer will sometimes correct me, and look at me strangely as if they are wondering how stupid can I be, if I can't tell the difference?
It's not that I can't tell the difference, it's that I didn't notice, because I don't care.
Is this normal, or am I an oddball?